1. Field of the Invention
The present invention relates to a method for supplying a cover gas used to prevent oxidation or combustion at the surface of a melt of magnesium or magnesium alloy (abbreviated as “magnesium” below).
Priority is claimed on Japanese Patent Application No. 2006-299051 filed on Nov. 2, 2006, the contents of which are incorporated herein by reference.
2. Description of the Related Art
The applicant of the present application suggested a gas containing fluoroketone and carbon dioxide gas as a cover gas in Japanese Unexamined Patent Applications, First Publication Nos. 2004-276116 and 2005-171374. Since the cover gas disclosed in those documents contains fluoroketone having a global warming potential lower than that of sulfur hexafluoride which has been used, the cover gas is expected to be used practically.
However, since fluoroketone is more expensive than sulfur hexafluoride, it is required to use it at low concentrations in the cover gas. Therefore, there is a case in which preventive effects of oxidation-combustion to the melt of magnesium decrease.
Therefore, the object of the present invention is to provide a method for supplying a cover gas which has sufficient preventive effects of oxidation-combustion and prevents cost-increase by containing a necessary and sufficient amount of fluoroketone in the cover gas which is supplied in a melting furnace of magnesium.